Method for cleaning gas-swept heating surfaces



M y 1957 B. o. BROMAN 2,792,316

METHOD FOR CLEANING GAS-SWEPT HEATING SURFACES Filed Feb. 1, 1954. 2Sheets-Sheet l N Fig. l {f May 14, 1957 B. o. BROMAN METHOD FOR CLEANINGGAS-SWEPT HEATING SURFACES 2 Sheets-Sheet 2 Filed Feb. 1, .1954

12/12 nitor METHQD FOR CLEANlNGGAS-SWEPT HEATING 1 SURFACES Bror QlofBroman, Stora Essingen, Sweden, assignor to glrtigbolaget A. EkstromsMaskinalfar, Stockholm,

we on Application February 1, 1954, Serial No. 407,439

Claims priority, application Sweden February 2, 1953 .3 Claims. (Cl,134-7) to pick up by such impact any material'deposits on the heatexchange surfaces and to prevent the accumulation of suchdeposits orcoatings.

The arrangement of the present invention constitutes an improvement overthe method and apparatus disclosed in my prior Patents 2,665,118,Apparatus for Cleaning Gas-Swept Heating Surfaces, and 2,665,119, Methodand Apparatus for Cleaning Gas-Swept Heating Surfaces, both issuedJanuary 5, 1954.

Additionally, the present inventionincorporates some of the arrangementembodied inmy prior filed application Serial No.'320,333'filed November13, 1952, and entitled Apparatus forDistributing Cleaning Particles OverGas-Swept Surfaces in Heat Exchangers and the Like.

In following the teachings of my prior patents, the cleaning pellets orshot which have been eflectively distributed within the casing of theapparatus to be cleaned and have cascaded therethrough, \are collectedat the bottom of the casing and conveyed back to the top of theapparatus by a cool air current usually induced by a suction fan. Thisair current partially reconditions the particles by burstingoif'deposits therefrom. Above the apparatus to be cleaned is a cycloneseparator into which the pellets and the burst-off deposits accompanyingthe same are introduced and'the pellets separated from the deposits andre-introduced into the apparatus to be cleaned While the conveying fluidis drawn off from the cyclone.

Usually the cleaning period is rather brief, that is, the period duringwhich the. shotpellets flow through the apparatus to be cleaned. In theinterval of the cleaning periods, there. is no flow of cleaning pelletsin either direction. Since the efficiency of the cleaning action isdependent upon a. certain intensity of the rain or the flow of pelletsimpingingagainst the heating surfaces, the fan means and conduits whichrecycle the pellets must be so dimensioned as to Warrant the maintenanceof a suflicient rate of flow of pellets back to the top of the apparatusto be cleaned during the cleaning period. Consequently, it is necessaryto use powerful machinery during the short cleaning period interval toensure the proper flow of pellets in the complete cycle.

Additionally, when the heating surfaces to be cleaned are of largedimensions, a plurality of complete cleaning units each having its ownpellet distributor, circulating system and fan means, have to beemployed to ensure satisfactory cleaning over the complete extent of theheating surfaces to be cleaned. .It will,. therefor e, .be appreciatedthat a completecleaning system for a large nited States Patent apparatussuch as a large boiler or heat exchanger will entail operation with ahigh rate of flow of the cleaning pellets and the necessity for aplurality of distributor devices, fan means and the like, will require ahigh monetary investment and also the utilization of high poweredmachinery for the operation of the complete system.

Accordingly, the present invention has for an object to provide a methodfor cleaning gas-swept heating surfaces of heat exchangers and the likeof economical initial cost and operation regardless of the dimensions ofthe heating surfaces to be cleaned.

Additionally, this invention has for an object to provide a method forcleaning gas-swept heating surfaces in which solid cleaning particles,such as shot pellets, are introduced through the top of the apparatus tobe cleaned and above the heating surfaces therein are distributedthroughout the cross-sectional area of the apparatus so that the theparticles impact or impinge and ricochet against the surfaces to becleaned, cascade through the apparatus, and return to the starting pointabove the apparatus for recycling through the apparatus in which theconveyance or return of particles to the starting position above theapparatus is effected over a duration of time considerably longer thanthe time duration of the actual cleaning period.

As a specific object, this invention provides a method in which thecleaning particles are distributed within and passed through theapparatus to be cleaned during short cleaning periods while the returnof particles to the source of supply is at a continuous rate.

Following the teachings of the present invention in the cleaning ofgas-swept surfaces of heat exchange apparatus by the cascading of solidcleaning particles such as shot pellets through the apparatus from topto bottom and recycling the pellets, the bulk of the cleaning pelletsnecessary to sustain an intense bombardment against the heating surfacesare conveyed from the bottom of the heat exchange apparatus back to thesource of supply of pellets at a much lower rate than the rate at whichthe pellets drop against the heating surfaces during actual cleaningperiods. Consequently, the fan means and the conduits necessary forconveying the pellets back to the source of supply are reduced asregards their dimensions and in some instances as regards the number ofsuch units. Therefore, a substantial saving in dimensions, materials andinvestment costs is effected and with the lowered operating power factorand the continuous or extended operation of the return phase of thecycle, the load caused by operating the fan means will be greatlyreduced.

It is a further particular object to provide compact apparatus whichwill accomplish the afcregoing extended return phase of the cleaningcycle.

Further and more specific objects will be apparent from the accompanyingdrawings, in which:

Figure 1 is a diagrammatic front elevational view of the heat exchangeapparatus embodying the cleaning system of the present invention, and

Figure 2, is a diagrammatic, side clevational view of the apparatusillustrated in Figure 1.

In the drawings, similar parts are identified with the same referencenumerals forthe purposes of comparison. In the figures, the referencenumeral it) denotes a heat interchanging apparatus associated with aboiler plant including a casing embodying side walls and a top Wall.

An upper gas inlet communicates with the casing through a side wallthereof at an area adjacent the top wall and plural lower gas outletscommunicate with each casing adjacent the lower extremity thereof.Within the casings are arranged, as indicated in my prior patents andapplication, tube means constituting theheat exchange surfaces.

The tubemeans are not illustrated inthis application since they form nopart of the present invention merely constituting the surfaces to becleaned. In the system embodied in my prior patents and application, theheating surfaces are kept clean and free of dust deposits and adherentcoatings by means of cleaning units each including a cyclone separator,the lower outlet of which communicates through bifurcated ducts ordistributing tubes that pass through the top of the casing and terminateabove the heating surfaces to be cleaned. Beneath the lower end of thedistributing tubes are deflection members as embodied in my priorapplication Serial No. 320,333. It follows that the cleaning pelletspassing through the tubes strike the deflection members and aredistributed throughout the cross-sectional area of the casing.

A conveying conduit communicates with each cyclone separator and extendsfrom the separating means that is disposed beneath the casing. Thepellets pass from the heating systems within the casing downwardly intopockets at the lower end of the casing and pass into separating meanswhere soot aggregates are separated from the pellets before the same arefed into the conveying conduit. This conduit has an open intake end andthe outlet of the cyclone communicates with a suction conduit connectedto a suction fan. it is clear that, in these prior embodiments withcontinuous operation during the relatively short cleaning period, highpower factors and large conduit dimensions are necessary to attain anefiective return rate of pellets from the separator means back to thecyclone separator for re-introduction into the casing.

By comparison with the aforedescribed installation, the one illustratedin Figures 1 and 2 is provided with a single cyclone separator 11 ofgreater capacity than the cyclone of the prior installation. From thiscyclone 11' a plurality of distributing tubes 12 extend downward andpass through the top of the casing and as shown in Figure 2 deflectionmembers 13 are disposed beneath the outlet ends of each tube 12'. At thebottom of the casing, the pockets 17, only two of which are used incomparision with the three embodied in the prior referred toarrangements, receive the pellets and feed them to the separating means18 from whence they are fed or injected into the conduit 14. Thisconduit has an open end to establish an air current therethrough andleads to the separator 11'. The outlet of the separator 11 feeds to asuction conduit is communicating with suction fan or pump means 16, thecapacity of which may be equal to or even less than the capacity of thefan 16 embodied in the installation referred to above. The cleaningoperation in those installations, that is the complete cycle, iscontinued during the cleaning intervals. This means that a comparativelyvery high or great volume of pellets is circulated during any givenlength of time while actual cleaning is occurring. During the intervalsbetween the cleaning periods, there will be no conveyance or recyclingof pellets. In the arrangement embodied in Figures 1 and 2 the suctionfan 16 may operate continuously or in any case over extended periods oftime so that the entire volume of cleaning particles or pellets thataccumulate in pockets 17 after a cleaning period are progressivelyconveyed back to the cyclone separator 11'. When actual cleaning is tooccur a valve member that is mounted beneath the bottom cyclone outlet,which valve is not shown in the drawings, is open and a bulk of cleaningpellets may distribute progresisvely against the deflection members 13and subsequently against the heating surfaces. The cleaning action willbe equal to or of greater intensity than that in'the prior installationsand the power consuming return phase of the cycle will be extended overmuch greater duration of time and thus a fan means with a lower outputcan be utilized. Since only one large cyclone separator, one fan andfewer conduits are needed in following this method, the investment costsare substantially reduced.

As an example of the effectiveness of the present invention, it ispointed out that in an instance where the heatturn period is'ofseven-hour duration.

ing surfaces to be cleaned have a total area of 50 m? and the height towhich the pellets must be returned 1s 25 m. and if the heating plant isa coal-fired boiler, an intensity of 200 kgs. pellets per in. per hourmay be adequate. It thus follows that a capacity of 10,000 kgs. pelletsper hour is required of the fans. If each fan can convey 2700 kgs.pellets per hour, then four fans are required and they can thus convey10,800 kgs. per hour. This factor is involved in a cleaning period whichextends for one hour and in which the pellets are continuously returnedto the top of the apparatus.

In carrying out the present invention, the cleaning period will still bean hour but there will be a seven-hour interval between cleaningperiods. In this instance a single fan with a capacity of 2700 kgs. perhour will convey 18,900 kgs. of pellets in this seven-hour period fromthe enlarged pocket area at the bottom to the enlarged cyclone at thetop. If these 18,900 kgs. of pellets are released during the hourcleaning period a more intense bombardment of the cleaning surfaces isattained than in the instance where the four fans which operate onlyduring the actual cleaning period but only have a total capacity toconvey 10,800 kgs. of pellets.

It is therefore clear that the present invention embodies the controlledfeeding through the valve, not shown, of the pellets and theintroduction and distribution of pellets into the casing of theapparatus to be cleaned so that the pellets cascade therethrough toclean the heating surfaces, the collection of the pellets beneath theflue gas outlet of the casing and the return of the pellets to thesource of supply over an extended period of time and at a reduced rateas compared with the rate of travel through the casing during thecleaning operation.

Thus and in accordance with the example given above, a cleaning periodis of one-hour duration while the re- Therefore, the cycle between startof cleaning and the re-accumulation of the supply of pellets for thenext cleaning is eight hours.

Therefore in accordance with this invention, 1 have provided a methodfor cleaning gas-swept heating surfaces of heat interchanging apparatusduring the operation thereof. The apparatus is of the type embodyingwalls and inlets and outlets for the gas and means that provide heatexchange surfaces within the walls. The method consists essentially ofcontrollably feeding cleaning particles, preferably shot pellets, froman accumulator position above the apparatus and introducing andsimultaneously spreading the pellets within the walls of the casing at apredetermined rate and at a level above the surfaces to be cleanedthroughout substantially the cross-sectional area comprised between thewalls so that the pellets fall by gravity and ricochet against thesurfaces to be cleaned to pick up material accumulated thereon anddislodge particles of material therefrom. The pellets are collectedbeneath the surfaces that have now been cleaned and also beneath the gasoutlet and are then entrained in a confined gaseous current andprogressively returned to the accumulator at a rate substantially slowerthan the rate of passage through the apparatus so that the cleaningparticles or pellets accumulate at the source for use during asubsequent cleaning operation. Additionally, during the return to thesource, the material that is accumulated on the pellets during passagethrough the apparatus and any material accompanying the pellets such asthose deposits burst off from the pellets under the action of theconfined gaseous current when the same is cool air, are separated fromthe pellets before they are accumulated and in readiness for asubsequent cleanmg operation.

Thus the accumulator can preferably constitute :1 cyclone separatorhaving substantial capacity so that it constitutes a combined separatorand accumulator and the source of supply for the particles or pellets.Beneath the separator is a distributing means that distributes pelletsthrough a plurality of tubes each communicating with a portion of theapparatus to be cleaned through the top thereof and each terminatingabove the surfaces to be cleaned. Operatively associated with the lowerend of each tube is a deflection member which deflects the pelletsfalling through the tube so that they are effectively distributedthroughout substantially the cross-sectional area comprised between thewalls of the apparatus. Beneath the heat interchanging apparatus, thatis, connected thereto at a level below the flue gas outlet or outlets,are suitable collecting pockets which feed to separators that separatelarger particles of material or dust from the pellets and which in turnalso feed the pellets so that they are entrained in a confined stream ofgaseous medium, preferably cool air, the air current being establishedby a suitable suction fan that communicates with the upper outlet of thecyclone separator so that the pellets are conveyed back to the cycloneseparator and any material accompanying the same or burst olf therefromunder the action of the cool air is separated in the separator and ledoff with the exhaust from the suction fan for any desired treatmentwhich can comprise the recovering of useful components from the materialdislodged from the heating surfaces within the apparatus.

What is claimed is:

1. A method of cleaning gas-swept heating surfaces of heat interchangingapparatus comprising feeding solid cleaning particles for a given periodof time only from a source of supply above the apparatus anddistributing the particles within the apparatus at a predetermined rate,above the surfaces to be cleaned and throughout substantially thecross-sectional area of the apparatus so that the particles cascadethrough the apparatus by gravity and impact and ricochet against thesurfaces to be cleaned to pick up material accumulated thereon and todislodge particles or material therefrom, separating at least most ofthe material from the particles, collecting the particles beneath thesurfaces, entraining the particles in a confined gaseous current andreturning the particles to the source for a period substantially inexcess of the period of feed with the rate of return being substantiallyslower than the rate of passage through the apparatus so that cleaningparticles accumulate at the source for use during a subsequent cleaningoperation.

2. A method of cleaning the gas-swept heating surfaces of heatinterchanging apparatus which apparatus is of the type embodying wallsdefining a casing and means providing heat exchange surfaces within thecasing and gas inlet and outlet means communicating with the casing,

comprising feeding a supply of metallic cleaning particles from a sourceof supply above the apparatus and introducing and simultaneouslyspreading the cleaning particles within the apparatus at a level abovethe surfaces to be cleaned and throughout substantially thecrosssectional area thereof so that the particles cascade through theapparatus and impact and ricochet against the surfaces to be cleaned topick up material accumulated thereon and to dislodge material therefromwith the particles passing through the apparatus at a rate and inquantity governed by gravity and the duration of the feeding period,ceasing the feed of particles, separating at least part of the materialfrom the particles, collecting the particles from beneath the surfaces,entraining the particles in a confined gaseous current with the rate ofentraining being less than the rate of passage through the apparatus andreturning the cleaning particles to the source at a rate consistent withthe rate of entrainment and substantially slower than the rate ofpassage through the apparatus whereby the cleaning particles accumulateat the source for use during a subsequent cleaning operation.

3. In the method of cleaning gasswept surfaces of heat interchangingapparatus of the type which includes the steps of feeding shot pelletsfrom the source of supply located above the apparatus to be cleaned anddistributing the pellets throughout substantially the cross-sectionalarea of the apparatus at a level above the surfaces so that the pelletscascade through the apparatus and impinge and ricochet against thesurfaces to pick up material accumulated thereon and to dislodgematerial therefrom so as to clean the same and in which method at leastthe pellets are collected at a level beneath the surfaces and returnedto the source of supply, the improvements comprising feeding pellets sothat they pass through the apparatus for a predetermined period of time,ceasing the feed of pellets, returning the pellets to the source duringand after the period of feed for a period of time substantially inexcess of the period of feed and at a rate substantially lower than therate of passage through the apparatus whereby the pellets accumulate atthe source for use during a subsequent cleaning period so that with eachperiod of feed being considerably shorter than the preceding period ofreturn an intensified cleaning action ensues.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD OF CLEANING GAS-SWEPT HEATING SURFACES OF HEAT INTERCHANGINGAPPARATUS COMPRISING FEEDING SOLID CLEANING PARTICLES FOR A GIVEN PERIODOF TIME ONLY FORM A SOURCE OF SUPPLY ABOVE THE APPARATUS ANDDISTRIBUTING THE PARTICLES WITHIN THE APPARTUS AT A PREDETERMINED RATE,ABOVE THE SURFACES TO THE CLEANED AND THROUGHOUT SUBSTANTIALLY THECROSS-SECTIONAL AREA OF THE APPARATUS SO THAT THE PARTICLES CASCADETHROUGH THE APPARATUS BY GRAVITY AND IMPACT AND RICOCHET AGAINST THESURFACES TO BE CLEANED TO PICK UP MATERIAL ACCUMULATED THEREON AND TODISLODGE PARTICLES OR MATERIAL THEREFROM, SEPARATING AT LEAST MOST OFTHE MATERIAL FROM THE PARTICLES, COLLECTING THE PARTICLES BENEATH THESURFACES, ENTRAINING THE PARTICLES IN A CONFINED GASEOUS CURRENT ANDRETURNING THE PARTICLES TO THE SOURCE FOR A PERIOD SUBSTANTIALLY INEXCESS OR THE PERIOD OF FEED WITH THE RATE OF RETURN BEING SUBSTANTIALLYSLOWER THAN THE RATE OF PASSAGE THROUGH THE APPARATUS SO THAT CLEANINGPARTICLES ACCUMULATE AT THE SOURCE FOR USE DURING A SUBSEQUENT CLEANINGOPERATION.